* New AP considerations emerge with 802.11g
You’ve likely heard that last month, the 802.11g Task Group ratified the 802.11g standard and that the IEEE 802 Executive Committee and IEEE Standard Board could give it their final OK as early as this week. With three officially sanctioned standards in the wireless LAN marketplace, what are the implications for your access point infrastructure?
802.11g, which specifies an aggregate of 54M bit/sec shared bandwidth in the 2.4 GHz frequency range, was developed for backward-compatibility with 11M bit/sec 802.11b. Going forward, then, you can install G APs for the higher speeds and still accommodate your B client base.
There are a couple of issues, though:
* Channel limitations could provoke interference.
* B clients hinder the performance of G networks.
With B and G APs, you remain limited to three nonoverlapping channels, making it difficult to avoid interference. If you create abutting or overlapping coverage cells that each use a different channel, the farthest away two same-channel cells can be is about a diameter’s width of a cell space, or between about 60 to 300 feet.
Also, once a B client associates with a G-based AP, G transmission speeds fall from about 23M bit/sec actual throughput to about 14M bit/sec – even if the B client is not transmitting, Atheros Communications President and CEO Craig Barratt states. The chipmaker recently introduced tri-mode chipsets with 802.11a/b/g support and Advanced Encryption Standard (AES) hardware support for compliance with the forthcoming 802.11i security standard.
802.11g networks slow down because they are designed to automatically go into “protected mode” in the presence of a B client. A special clear-to-send header is appended to G packets so B packets can detect – and avoid – G traffic, Barratt explains. But this also clutters up the network with additional overhead.
What can help is adding 802.11g’s cousin, 802.11a, into the AP mix. 802.11a offers the same speed as G but in a different frequency (the 5 GHz band) and with many more nonoverlapping channels. Depending on geography and the outcome of this year’s World Radiocommunication Conference in Geneva, Switzerland (occurring now), the three B and/or G channels could be combined with, eventually, as many as 24 5 GHz channels, so interference can be easily avoided.
